Accumulated carbon loss

Figure 15. Predicted accumulated carbon loss distribution along anode flow-field over a complete start-stop cycle for a controlled start-stop experiment as shown above the plot at 80 °C, 101 kPaabs, 66% RHjn, and residence time of 1.5 s based on anode void volume (including flow-field and diffusion medium). The model predicts nearly symmetric carbon loss at anode inlet and outlet because the stop process essentially mirrors the start process by switching H2 and air periodically at anode inlet.

Recent kinetic studies indicate that carbon corrosion can be significant under normal transient operation.56,57,60-62 The rate of voltage change, common in the automotive application, enhances cathode carbon-support corrosion.16 Hence, further model improvement shall be focused on finding the carbon corrosion kinetics associated with voltage cycling. Currently, the relationship between fuel cell performance decay and accumulated carbon-support loss is only empirical.22 More effort has to be made to incorporate mechanisms that can accurately quantify voltage decay with carbon-support loss.31,32... 

While the seafloor depths of the lysocline and CCD can be readily identified from sedimentary criteria, this information is of limited use without realistic knowledge of the rates at which calcium carbonate is lost from the sediments to dissolution. In practice, it is much easier to determine carbonate accumulation in the deep sea than it is to estimate carbonate loss. Yet the latter information is clearly needed in order to close sediment budgets and to reconstruct changes in the carbonate system. 

Further insight is gained if the performance loss upon start/stop cycling is correlated with the accumulated total carbon loss at 0.1 and 0.7 A cm (Fig. 14.13a, b). At lower current densities, where kinetic ORR losses (A//orr) are dominant, it seems that the relationship between... 

Fig. 1 COj concentration (solid symbols) and accumulative carbon weight loss (open symbols, integrated from the CO flux at the exit of the working electrode) as a function of time over a commercial conventional-carbon-supported membrane electrode assembly (MEA). The N -fed working electrode (50 cm min" ) was held at a potential of 1.2 V versus the H -fed counter/reference electrode (200 cm min" ) at 95°C and 80% inlet relative humidity (RHj i j). RHE reversible hydrogen electrode...

The presence of active sulphate-reducing bacteria usually results in graphitic corrosion and this has led to a useful method of diagnosing this cause of corrosion. The leaching out of iron from the graphitic residue which is responsible for the characteristic appearance of this type of corrosion leads to an enriched carbon, silicon and phosphorus content in the residue as compared with the original content of these elements in the cast iron. Sulphur is usually lost to some extent but when active sulphate-reducing bacteria are present, this loss is offset by the accumulation of ferrous sulphide in the residue with a consequent increase in the sulphur content of the residue out... 

A traditional system for the preparation of table olives, involves a treatment of the fresh fruit with a solution of NaOH to hydrolised the bitter glycoside oleuropein, followed by a lactic fermentation in brine. The modifications that take place on pectic polysaccharides of olives (Manzanilla variety) during this process was smdied. Processing induced a net loss of polysaccharides soluble in sodium carbonate and a paralel accumulation of water and Imidazole/HCl soluble polysaccharides. A general decrease of the apparent molecular weight of water and carbonate soluble polysaccharides was also detected. 

When the amount of coke formed as a function of time on stream is compared to the decrease in catalytic activity (see Fig. 3), two regimes of deactivation can be noticed for the strongly deactivating catalysts, i e, a slow initial deactivation which is followed by a rapid loss of activity This first phase is characteristic of a slow transformation of the reactive carbon into less reactive coke. The second phase is attributed to carbon formed on the support which accumulates there and rapidly covers the Pt particles when its amount reaches a critical value causing the sudden decay of catalytic activity. 

Group 2 Coke imbalance. This grouping considers malfunctions leading to a difference between the rate at which coke accumulates on the catalyst and the rate at which it is burned off. A coke imbalance is associated with a reduction of oxygen, which can be caused by a loss of combustion air or through an increase in the conradson carbon in the gas oil feed to the unit. 

For solids run-off it is assumed that this run-off water contains 200 parts per million by volume of solids thus the corresponding velocity term U12 is 200 x 10 6t Jn, i.e., 10 s m/h. This corresponds to the loss of soil at a rate of about 0.1 mm per year. If these solids were completely deposited in the aquatic environment (which is about l/10th the soil area), they would accumulate at about 0.1 cm per year, which is about a factor of four less than the deposition rate to sediments. The implication is that most of this deposition is of naturally generated organic carbon and from sources such as bank erosion. 

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